1. Field of the Invention
The present invention relates to systems which monitor both airway carbon dioxide concentration and respiratory flow. Specifically, the present invention relates to systems which monitor respiratory air flow, pressure and carbon dioxide levels, process those measurements to derive information about various respiratory-related functions and blood carbon dioxide levels, and display the measured and derived information.
2. Background of Related Art
Respiratory monitors are known in the art. Typically, respiratory monitors measure respiratory air flow rates at discrete sampling intervals. Many respiratory monitoring apparatus process respiratory samples to determine characteristics such as respiratory rate and depth of respiration. U.S. Pat. No. 5,273,036, issued to Harald Kronberg and Helmut Leist on Dec. 28, 1993 and U.S. Pat. No. 4,989,456, issued to Josef Stupecky on Feb. 5, 1991, disclose exemplary devices.
However, many respiratory monitors in the prior art sample only a limited aspect of a patient""s respiration and display a limited number of directly measured respiratory characteristics rather than an overall profile of a patient""s respiration. Moreover, many existing respiratory monitors do not allow a user to select the displayed respiratory profiles.
A system is needed which monitors a variety of respiratory profile parameters and displays data regarding those parameters. There is also a need for a system which, following measurement of some respiratory parameters, automatically generates data regarding other respiratory profile parameters.
The system of the present invention addresses the foregoing needs. The system of the present invention includes an apparatus which utilizes software to process respiratory pressure, flow, volume and gas content information and preferably displays such types of information in the forms of numeric values and graphs. The system of the present invention also processes the measured information in order to calculate or otherwise determine a wide variety of respiratory profile characteristics which are not directly measurable by noninvasive means.
In a preferred embodiment of the method of the present invention, respiratory measurements are taken at discrete time intervals. Preferably, respiratory samples are taken about once every 0.01 seconds (10 milliseconds). The respiratory measurements taken during each sample include, but are not limited to, the respiratory flow rate, respiratory pressures, respiratory carbon dioxide level, and other respiratory or respiratory-related characteristics. Blood oxygen saturation may also be measured by the system of this invention. Pulse oximetry methods which are known to those in the art are preferred for measuring blood oxygen saturation in connection with the present invention. Each piece of data is either sampled digitally or sampled by analog means, then digitized immediately following sampling. Methods and mechanisms for digital sampling and digitization of analog samples which are known to those of ordinary skill in the art are useful in the system of the present invention.
During respiratory monitoring and sampling, the system of the present invention calculates various respiratory profile characteristics, including, without limitation, the timing of the respiratory cycle and its intervals, respiratory flows and volumes, respiratory pressures, and carbon dioxide levels in the breath. The derivation of carbon dioxide and oxygen levels in a patient""s arterial blood are also within the contemplated scope of the present invention. If a patient""s respiration is controlled by a ventilator, the system of the present invention may also calculate respiratory mechanics characteristics.
Other advantages of the respiratory profile parameter processing and display system of the present invention will become apparent to those of skill in the relevant art through a consideration of the ensuing description and the appended drawing figures.